Non-stick coatings that reversibly change colour responsive to a temperature change have many applications, for instance, in cookware such as pots, pans and cooking utensils, as well as in various types of heaters (e.g. wood burning stoves, heating boilers, infra-red heaters etc), fans, refrigerators, irons, building materials, health aids, personal care products such as hair straighteners, curling tongs, and industrial products, etc.
A problem in the art is that the coatings for use in cookware need to withstand temperatures of at least 200° C., whilst maintaining a non-stick function and without degradation of the incorporated thermochromic agents. Colour change agents of the art rely at least on organic pigments, for instance, perylene red, which are affected by the high temperatures such that the colour change becomes irreversible. Alternatively, the colour change agent may be affected by cooking ingredients such as oils that taint the coating unevenly, and give the appearance of an unclean surface. Degradation of the coating can lead to the release of toxins, which are to be avoided in any cookware applications. Furthermore, the extent of colour change in the art is often not sufficient to discern a colour change, thereby requiring the presence of two patterns that change colour differentially upon heating to obtain a visible contrast (e.g. U.S. Pat. No. 6,551,693 B1). The pattern is limited in area to a central medallion that reflects the pan temperature only at one location, while the periphery of the pan may be at an insufficient temperature.
In view thereof, there remains a need in the art for further and/or improved thermally colour-changeable ceramic coating compositions for instance for use on any artefact, in particular for non-stick coatings, in particular on a cookware item.
The present coating compositions and coatings aim to overcome the problems in the art.